linux-kernel - Re: [PATCH v11 5/6] dmaengine: pl330: Add PM sleep support

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Date:	Thu, 13 Nov 2014 02:37:52 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
Cc:	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	Russell King <linux@....linux.org.uk>,
	Dan Williams <dan.j.williams@...el.com>,
	Vinod Koul <vinod.koul@...el.com>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Alan Stern <stern@...land.harvard.edu>,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	dmaengine@...r.kernel.org, Kevin Hilman <khilman@...nel.org>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH v11 5/6] dmaengine: pl330: Add PM sleep support

On Wednesday, November 12, 2014 03:32:27 PM Krzysztof Kozlowski wrote:
> Add system suspend/resume capabilities to the pl330 driver so the amba
> bus clock could be also unprepared to conserve energy.
> 
> Signed-off-by: Krzysztof Kozlowski <k.kozlowski@...sung.com>
> ---
>  drivers/dma/pl330.c | 37 +++++++++++++++++++++++++++++++++++++
>  1 file changed, 37 insertions(+)
> 
> diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c
> index c3bd3584f261..fd71777fc565 100644
> --- a/drivers/dma/pl330.c
> +++ b/drivers/dma/pl330.c
> @@ -2627,6 +2627,42 @@ static int pl330_dma_device_slave_caps(struct dma_chan *dchan,
>  	return 0;
>  }
>  
> +/*
> + * Runtime PM callbacks are provided by amba/bus.c driver.
> + *
> + * It is assumed here that IRQ safe runtime PM is chosen in probe and amba
> + * bus driver will only disable/enable the clock in runtime PM callbacks.
> + */
> +static int __maybe_unused pl330_suspend(struct device *dev)
> +{
> +	struct amba_device *pcdev = to_amba_device(dev);
> +
> +	if (!pm_runtime_status_suspended(dev)) {

It generally isn't safe to call that in .suspend(), because the status may still
change in theory.  On the other hand, if you do that in .suspend_late(), you'll
be safe from that.

> +		/* amba did not disable the clock */
> +		amba_pclk_disable(pcdev);
> +	}
> +	amba_pclk_unprepare(pcdev);
> +
> +	return 0;
> +}
> +
> +static int __maybe_unused pl330_resume(struct device *dev)
> +{
> +	struct amba_device *pcdev = to_amba_device(dev);
> +	int ret;
> +
> +	ret = amba_pclk_prepare(pcdev);
> +	if (ret)
> +		return ret;
> +
> +	if (!pm_runtime_status_suspended(dev))
> +		ret = amba_pclk_enable(pcdev);
> +
> +	return ret;
> +}
> +
> +static SIMPLE_DEV_PM_OPS(pl330_pm, pl330_suspend, pl330_resume);
> +
>  static int
>  pl330_probe(struct amba_device *adev, const struct amba_id *id)
>  {
> @@ -2853,6 +2889,7 @@ static struct amba_driver pl330_driver = {
>  	.drv = {
>  		.owner = THIS_MODULE,
>  		.name = "dma-pl330",
> +		.pm = &pl330_pm,
>  	},
>  	.id_table = pl330_ids,
>  	.probe = pl330_probe,
> 

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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